Runway Lighting Photometry: Intensity, Coverage, Colour & Testing
How photometry measures the intensity, distribution, colour and alignment of runway edge, threshold, end, centreline, touchdown zone and approach lights. A runway light can be switched on and still give too little output, the wrong beam pattern or the wrong direction.
What Is Runway Lighting Photometry?
Runway lighting photometry is the measurement and evaluation of the optical performance of runway lighting fixtures. It shows whether installed lights give the intensity, distribution, colour and alignment their operational function needs, and it answers a different question from "is the lamp on?"
Why on/off is not enough
Two runway edge lights can look alike during a night inspection while one has much lower output or a displaced beam. Photometry finds differences that visual inspection cannot judge reliably.
When it is carried out
Commissioning, periodic inspection, preventive maintenance, rehabilitation, troubleshooting, and after replacement of runway lighting equipment.
Depending on the fixture and test requirement, measurements may examine
Why Runway Photometry Is Important
Runway lights form a visual guidance system, and their usefulness depends on the pilot receiving a consistent and unambiguous visual pattern. A photometry programme supports both compliance verification and condition-based maintenance.
Low intensity
A lamp, LED assembly or optical system can degrade while still operating.
Misalignment
The fixture produces light, but the main beam may no longer point the right way.
Contaminated optics
Rubber deposits, dirt, dust and moisture cut output, especially for in-pavement fixtures.
Incorrect colour
Lenses, filters or light sources can deteriorate and move colour out of requirement.
Incorrect installation
A replacement fixture or optical assembly may be oriented or installed wrongly.
Uneven performance
Individual fixtures can drift away from the rest of the lighting system.
Planning a Runway Photometry Programme
Plan around the runway configuration, lighting system, operational category, equipment type and inspection requirements. A typical programme runs from drawing review to the final report.
Commissioning
After new installation, rehabilitation or major modification. Sets the baseline.
Periodic
Monitors installed performance during operation and builds a history.
Maintenance
Locates fixtures that need cleaning, adjustment, repair or replacement.
Acceptance
Shows installed equipment meets project or authority requirements.
Troubleshooting
Used when intensity looks inconsistent or misalignment is suspected.
What to Test on Each Runway Fixture Type
Pick a fixture type to see what the test should cover. This is a planning aid, and the approved specification sets the actual parameters and limits.
Test should consider
Watch for
Runway Edge, Threshold, End, Centreline, Touchdown and Approach Lights
Each light type has a different optical function, so the measurement method and acceptance criteria must match the fixture and the runway configuration.
| Light type | Primary function | Particular test attention |
|---|---|---|
| Edge | Lateral guidance | Orientation relative to runway geometry; in-pavement fixtures add lens contamination and water |
| Threshold | Marks the start of the usable landing portion | Direction, intensity and distribution as well as colour |
| Runway end | Marks the runway end; may be bidirectional | Test each viewing direction the fixture serves |
| Centreline | Longitudinal guidance | Optical window condition, contamination, spacing consistency |
| Touchdown zone | Guidance in the touchdown area | Adjacent-unit consistency, moisture and debris protection |
| Approach | Approach visual guidance | Complete pattern and array consistency, not single-fixture comparison |
A fixture that draws the correct electrical current but produces degraded optical output has not necessarily met its operational requirement.
Intensity, Colour and Coverage
Intensity
Depends on fixture design, light source, optics, operating step, beam direction, measurement geometry, environment and fixture condition. Controlled, repeatable conditions are required.
Colour
Intensity and colour are related but separate checks. A fixture with acceptable intensity can still have degraded colour from filter, lens or light-source ageing.
Coverage
Whether enough output is given over the required angular region. A high peak intensity can still fail the distribution.
Intensity at different brightness steps
Report the operating condition used (low, intermediate or high step, where those apply). Comparing a fixture measured at one step with a specification for another gives misleading results.
Absolute versus comparative
Absolute: the measured value is compared directly with a specified limit. Comparative: the result is compared with baseline, neighbouring fixtures or history, which can expose a progressive loss before a formal failure.
How Is Runway Light Intensity Measured?
Runway light intensity is measured with calibrated photometric test equipment under controlled, repeatable conditions. The fixture is inspected and, where the procedure permits, cleaned first. The sensor position, distance, viewing direction, height and fixture orientation are then fixed and recorded, and the circuit is set to the required brightness step. The reading is compared with the applicable acceptance criterion or with baseline data, using the same geometry each time. See the measurement procedure below for the full ten stages.
Analyse more than peak output
| Aspect | What it tells you |
|---|---|
| Peak output | Light produced in the principal measurement direction |
| Angular distribution | How output changes with viewing angle |
| Useful coverage | Whether intensity holds across the required beam region |
| Consistency | Whether adjacent fixtures give a comparable and appropriate pattern |
Colour evaluation may consider
Runway lighting plan: which lights are where.
AGL Visual Encyclopedia: Runway lighting layout Runway edge lights Threshold lights
Coverage as isocandela contours.
AGL Visual Encyclopedia: Isocandela diagram Photometric distribution Beam pattern
Runway Photometer, Calibration and Test Equipment
What a runway photometer does
An instrument or measurement system for the optical output of airport lighting fixtures. Depending on the equipment it measures or calculates luminous intensity, distribution, angular position, colour-related information, fixture orientation, beam characteristics and location. Mobile systems allow rapid measurement of runway installations and help locate deficient fixtures.
A typical system may include
Photometric sensor, optical sensor or camera, positioning, distance and angular measurement, data acquisition unit, computer or tablet, software, fixture identification database and calibration references. Mobile systems add location tracking and automated processing.
Before testing, verify
- Instrument identification and calibration status
- Calibration certificate, reference or traceability requirements
- Measurement range and sensor condition
- Software or data-acquisition configuration
- Date and time settings
Fixture on a rotating stage, photometer at a measured distance.
AGL Visual Encyclopedia: Photometer arrangement Photometric testing arrangement Automated photometry
Runway Photometry Measurement Procedure
A controlled test follows ten stages. Do not assume the same acceptance limits apply to every runway or fixture type.
Review the test requirements
Runway, lighting system, fixture types, scope, standards, specifications, acceptance criteria, operating settings and measurement points.
Review drawings and asset information
Layout, runway geometry, fixture schedule, datasheets, earlier photometric reports, maintenance history and as-builts.
Verify test equipment
Calibration, identification, software set-up, sensor configuration, range, date and time, data storage.
Inspect the runway lighting
Damaged lenses, contamination, missing fixtures, damaged housings, wrong orientation, water ingress, loose fittings, damaged cables or connectors, abnormal illumination. Clean before final acceptance measurements where the procedure permits.
Establish measurement geometry
Sensor position, distance, viewing direction, height, horizontal and vertical alignment, angle and fixture orientation. Use the same geometry when comparing.
Operate at the required setting
Set the specified test intensity and record the actual operating condition.
Measure the fixtures
Each fixture or the specified representative set, linked to runway, type, fixture ID, station, step, date and time, and result.
Evaluate the results
Compare with acceptance criteria and classify: pass, fail, investigate, maintenance required or retest required.
Correct deficiencies
Cleaning, optical adjustment, realignment, lens, lamp, LED module or fixture replacement, electrical troubleshooting, transformer or connector inspection, water-ingress correction.
Retest
Remeasure corrected fixtures. A light that is visible again is not proof of the required optical performance.
Test points depend on the fixture and specification
The measurement procedure at a glance.
AGL Visual Encyclopedia: Photometric testing process Photometric grid Measurement points
Common Photometry Failures and Troubleshooting
Click a failure to see the causes to investigate.
Low light intensity
Possible Cause
- Degraded lamp or LED
- Optical contamination
- Damaged lens
- Incorrect lamp type
- Ageing optical components
- Electrical problems
- Incorrect intensity step
Misalignment
Possible Cause
- Physical impact
- Incorrect installation
- Loose mounting
- Maintenance error
- Fixture movement
- Foundation or mounting problems
Dirty optical surfaces
Possible Cause
- Rubber deposits
- Dirt and dust
- De-icing materials
- Standing water
- Pavement debris
Water ingress
Possible Cause
- Optical degradation and condensation
- Electrical failures
- Corrosion
- Failed enclosure, gasket, lens seal or drainage
Incorrect replacement component
Possible Cause
- Wrong lamp, optical assembly or part altering the photometric output
- Lamps other than those approved for the fixture
Wrong operating current or brightness setting
Possible Cause
- Fixture measured at a different intensity step from the specification
- Operating condition not recorded in the test data
Electrical circuit problems
Possible Cause
- Poor connections
- Cable degradation
- Isolation transformer problems
- Connector faults
- Abnormal series-circuit conditions
- Incorrect regulator operation
Investigation sequence for an abnormal result
This sequence stops a team replacing a fixture when the real cause is contamination, alignment or an upstream electrical issue. The optical result also points troubleshooting toward either the fixture or the electrical system.
Related Guides
Troubleshooting Engine CCR working principle Airport isolating transformer Junction boxes and housingsFour common photometric failures as contours.
AGL Visual Encyclopedia: Photometric failure visualization Misalignment LED failure
Photometry and Alignment
How alignment errors arise
Vehicle impact, maintenance work, fixture replacement, pavement work, foundation movement, incorrect installation and mechanical loosening.
What photometry shows
An incorrectly aligned light can look bright from the wrong location. Photometric measurement shows whether the optical output is delivered in the intended direction, so use it together with runway geometry and fixture orientation data.
Why alignment changes the measured peak.
AGL Visual Encyclopedia: Fixture alignment in photometry Runway fixture alignment Alignment verification
Handling a Failed Photometric Result
A failed measurement is not automatically a failed fixture. Validate the measurement before assigning maintenance.
Check the measurement
- Test instrument calibration
- Test geometry
- Sensor alignment
- Operating intensity
- Fixture identification
- Measurement repeatability
Then check the fixture
- Contamination
- Physical alignment
- Optical condition
- Electrical condition
Retest after
Why retesting matters
Maintenance can fix one problem and introduce another: a lens replacement may alter output, a realignment may move the beam away from another required direction, a replacement lamp may differ optically, and a replacement fixture may mount at a different orientation.
Retest conditions
Where practical, retest under conditions comparable with the original measurement. Show success by measurement rather than assuming it.
Compare with limits, then pass or investigate.
AGL Visual Encyclopedia: Photometric compliance flow Photometric acceptance Before and after photometry
Commissioning, Periodic Testing and the Photometric Report
Commissioning baseline
Document installed fixture type, location, equipment ID, operating condition, measurement equipment, calibration status, measured performance, acceptance criteria, pass/fail result, corrective actions and final retest. The report becomes the baseline for later tests.
Periodic testing
Compare current and previous intensity, fixture-to-fixture variation, repeated fault locations, maintenance frequency and trends. Frequency follows authority requirements, airport conditions, equipment condition and the approved maintenance programme.
Example data table
| Fixture ID | Location | Fixture type | Intensity step | Measured result | Acceptance criterion | Result |
|---|---|---|---|---|---|---|
| RW-EL-001 | Runway edge | Edge light | Specified step | Recorded value | Applicable limit | Pass |
| RW-EL-002 | Runway edge | Edge light | Specified step | Recorded value | Applicable limit | Pass |
| RW-CN-001 | Centreline | In-pavement | Specified step | Recorded value | Applicable limit | Investigate |
Project and equipment
Airport, runway, reference number, date, conditions, organisation, personnel; photometer manufacturer, model, serial, sensor ID, calibration certificate and software version.
Lighting information
Fixture type, manufacturer, model, ID, location, installation type, operating intensity and relevant electrical configuration.
Five questions it must answer
What was tested, how, what was measured, what it should have been (with source), and what happened after a failure.
A good report records the full chain: measurement, defect, corrective action, verification. Record failures fixture by fixture, not as one runway pass/fail.
Reading a photometric report in six steps.
AGL Visual Encyclopedia: Report interpretation Data interpretation Photometric inspection
Photometry vs Visual Inspection
The two are complementary. A light that looks acceptable to an inspector may not meet its photometric requirement, so a maintenance programme uses both.
| Finding | Visual inspection | Photometry |
|---|---|---|
| Burned-out lights | Yes | Yes |
| Damaged fixtures and broken lenses | Yes | Limited |
| Contamination and water ingress | Yes | Shows the effect on output |
| Obvious misalignment | Yes | Yes |
| Reduced intensity | Subjective | Yes |
| Quantitative degradation | No | Yes |
| Beam displacement and distribution | Limited | Yes |
| Inconsistent performance and trends | Limited | Yes |
Where photometry sits in AGL maintenance
Related Guides
AGL testing and inspection Maintenance handbook CCR working principle Airport isolating transformer
Runway Lighting Photometry Checklist
Click an item to mark it complete.
Before testing
During testing
After testing
Runway Photometry Best Practices
Use calibrated equipment
Accuracy begins with controlled instrumentation.
Use repeatable geometry
Changes in sensor position create misleading differences.
Identify every fixture
Data must trace to an exact runway location.
Record the operating condition
Tie intensity results to the correct lighting step.
Clean before final acceptance
Contamination can artificially lower measured output.
Record failures individually
Do not report only an overall runway pass/fail.
Maintain historical data
Trend analysis shows deterioration.
Retest corrective work
Confirm a repair by measurement.
Reference the exact criteria
Identify the source of every requirement.
Recommended End-to-End Workflow
Run photometry as an asset-management tool across the life of the installation, not as a one-time acceptance activity.
Design review
Confirm fixture types and photometric requirements.
Installation
Verify physical and optical installation.
Pre-commissioning inspection
Check condition, orientation and cleanliness.
Photometric measurement
Measure intensity, distribution, colour and applicable optical parameters.
Acceptance evaluation
Compare with approved criteria.
Corrective action
Clean, align, repair or replace.
Retest
Verify the corrective action.
Baseline report
Establish initial performance data.
Periodic testing
Repeat measurements in service.
Trend analysis
Identify progressive degradation.
Standards and Acceptance Criteria
International SARPs for aerodrome design and operation, including visual aids. The ICAO Store lists the 9th Edition (July 2022) with Amendment 18 and later corrigenda.
Specification for runway, taxiway, heliport and vertiport light fixtures. Edition F (30 September 2024) is cited here.
Maintenance of Airport Visual Aid Facilities, including cleaning and photometric measurement.
Runway type, operational category, fixture type, approved equipment specification, project design and airport maintenance procedures.
Four checks feed one acceptance decision.
AGL Visual Encyclopedia: Photometric acceptance Photometric compliance flow Photometric performance
Quick Knowledge Check
Q1. Why can a runway light pass visual inspection and still fail photometry?
Q2. What should be done first after a fixture fails a photometric measurement?
Q3. Why must the operating intensity step be recorded?
Q4. What does comparative photometry compare a result with?
Q5. Why must a corrected fixture be retested?
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Open AGL Photometric Testing Guide →PAPI Engineering Guide
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From fixture identification to baseline reports and retesting, explore the complete AGL knowledge base for photometry and maintenance.
Explore the AGL Engineering Knowledge Hub
Fundamentals
Standards & Compliance
Runway, Taxiway & Approach Lighting
Surface Movement & Safety
PAPI
Electrical Engineering & Power
Photometry & Testing
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Resources, Documentation & Careers
Runway Lighting Photometry FAQ
Q1What is runway lighting photometry?
Runway lighting photometry is the measurement of the optical performance of runway lighting fixtures, including parameters such as intensity, distribution, colour and alignment.
Q2Why is runway photometric testing required?
It verifies that installed lights continue to give the intended visual guidance, and it finds degradation or misalignment that normal visual inspection may not reveal.
Q3What does a runway photometer measure?
Depending on the instrument and application, it can measure light intensity, distribution and other optical characteristics, and may also determine alignment or location information.
Q4How often should runway lights be photometrically tested?
There is no single universal interval. Follow the applicable authority requirements and the airport maintenance programme, considering runway usage, environmental conditions, equipment reliability and historical performance. FAA guidance lists traffic, pollution, equipment reliability and observed field performance as factors.
Q5Can photometry detect misaligned runway lights?
Yes. Photometric measurement can show that a fixture's optical output is not being delivered in the intended direction.
Q6Can a light pass visual inspection and fail photometry?
Yes. A fixture can stay illuminated while giving insufficient intensity, an incorrect beam pattern or other degraded optical performance.
Q7Why are in-pavement runway lights difficult to maintain?
They are exposed to contamination, rubber deposits, pavement loading, moisture and mechanical stress. These conditions can degrade optical performance even while the fixture keeps operating.
Q8Should runway lights be cleaned before photometric testing?
Where the test procedure requires it, clean before final acceptance measurements so contamination is not mistaken for fixture degradation.
Q9Is intensity alone enough to evaluate a runway light?
Not always. Depending on the applicable requirement, colour, distribution, beam coverage and alignment may also need to be evaluated.
Q10What should be included in a runway photometric report?
Runway and fixture identification, test date, equipment and calibration information, operating condition, measurement method, measured results, acceptance criteria, pass/fail status, corrective actions and retest results.
Q11What is the difference between absolute and comparative photometry?
Absolute photometry compares a measured value directly with a specified limit. Comparative photometry compares the result with a baseline, neighbouring fixtures or historical data, which can show a progressive loss of output before a formal failure.
Q12What should I do when a fixture fails a photometric measurement?
Validate the measurement first: instrument calibration, geometry, sensor alignment, operating intensity and fixture identification. Then check contamination, alignment, optics and the electrical supply before repairing or replacing, and retest afterwards.
Engineering & Expert Notes
Measure the Right Items
ScopeDefine which fixtures and parameters are tested for each part of the runway.
Record the Intensity Step
SettingsOutput varies with the step used. Always note it.
Check Alignment Alongside Intensity
AlignmentPoor aiming can give misleading readings.
Clean Optics Before Concluding
ContaminationDirt is a common cause of low readings. Clean and retest.
Handle Failed Results Methodically
FailuresVerify setup, then rectify and retest, keeping both sets of data.
Keep Raw Data
RecordsStore readings and test conditions with the report.
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